MICROCONTROLLER

INTRODUCTIONTO 8051

SANDEEP.KAMATHF.Y.IT ROLL NO.18

WHAT IS A MICROCONTROLLER?

• All of the components needed for a controller were built right onto one chip.

• Thus A one chip computer, or microcontroller was born.

• A microcontroller is a highly integrated chip which includes, on one chip, all or most of the parts needed for a controller.

• The microcontroller could be called a "one-chip solution".

Features :• The Intel 8051 is used in embedded

systems– 8-bit CPU– 4k bytes ROM for the program– 128 BYTES of RAM for variables– 32 I/O lines ( 4 PORTS WITH 8 EACH )– 2 timers– 1 Serial port– 6 interrupt sources– Low cost (25-30 Rs per chip)

Block Diagram

CPU

InterruptControl

OSC BusControl

4kROM

Timer 1Timer 2

Serial

128 bytes RAM

4 I/O Ports

TXD RXD

External Interrupts

P0 P2 P1 P3Addr/Data

8051 – PIN DIAGRAM

8051 – 40 PIN IC

• 8051 contains four I/O ports (P0 - P3)• Each port can be used as input or output

(bi-direction)

Port 0 P0（ P0.0～

P0.7）

8-bit R/W - General

Purpose I/O

Or acts as a multiplexed

low byte address and data bus for

external memory design

Port 1 P1（ P1.0～

P1.7）

Only 8-bit R/W -

General Purpose

I/O

Port 2 P2（ P2.0～

P2.7）8-bit R/W -

General Purpose I/O

Or high byte of the

address bus for

external memory design

Port 3 P3（ P3.0～

P3.7）

General Purpose I/O

if not using any of the

internal peripherals (timers) or

external interrupts.

IMPORTANT PINS

• PSEN (out): Program Store Enable, the read signal for external program memory (active low).

• ALE (out): Address Latch Enable, to latch address outputs at Port0 and Port2

• EA (in): External Access Enable, active low to access external program memory locations 0 to 4K

• RXD,TXD: UART pins for serial I/O on Port 3

• XTAL1 & XTAL2: Crystal inputs for internal oscillator.

SIGNALS - OPERATION

• Vcc （ pin 40 ）：– Vcc provides supply voltage to the chip. – The voltage source is +5V.

• GND （ pin 20 ）： ground• XTAL1 and XTAL2 （ pins 19,18 ）：

– These 2 pins provide external clock.– Way 1 ： using a quartz crystal oscillator – Way 2 ： using a TTL oscillator

RST - RESET

• RST（ pin 9）： reset– input pin and active high

• The high pulse must be high at least 2 machine cycles.

– power-on reset.

• Upon applying a high pulse to RST, the microcontroller will reset and all values in registers will be lost.

EA & PSEN

• EA（ pin 31）： external access– There is no on-chip ROM in 8031 and 8032 .– The EA pin is connected to GND to indicate the

code is stored externally.– PSEN ＆ ALE are used for external ROM.– active low.

• PSEN（ pin 29）： program store enable– This is an output pin and is connected to the OE

pin of the ROM.

ALE

• ALE（ pin 30）： address latch enableIt is an output pin and is active high.8051 port 0 provides both address and data.The ALE pin is used for de-multiplexing the

address and data by connecting to the G pin of the 74LS373 latch.

THANKYOU